DESCRIPTION

The rman set of functions provides a flexible resource management
abstraction. It is used extensively by the bus management code. It
implements the abstractions of region and resource. A region descriptor
is used to manage a region; this could be memory or some other form of
bus space.
Each region has a set of bounds. Within these bounds, allocated segments
may reside. Each segment, termed a resource, has several properties
which are represented by a 16-bit flag register, as follows.
#define RF_ALLOCATED 0x0001 /* resource has been reserved */
#define RF_ACTIVE 0x0002 /* resource allocation has been activated */
#define RF_SHAREABLE 0x0004 /* resource permits contemporaneous sharing */
#define RF_TIMESHARE 0x0008 /* resource permits time-division sharing */
#define RF_WANTED 0x0010 /* somebody is waiting for this resource */
#define RF_FIRSTSHARE 0x0020 /* first in sharing list */
#define RF_PREFETCHABLE 0x0040 /* resource is prefetchable */
The remainder of the flag bits are used to represent the desired
alignment of the resource within the region.
The rman_init() function initializes the region descriptor, pointed to by
the rm argument, for use with the resource management functions. It is
required that the fields rm_type and rm_descr of structrman be set
before calling rman_init(). The field rm_type shall be set to
RMAN_ARRAY. The field rm_descr shall be set to a string that describes
the resource to be managed. It also initializes any mutexes associated
with the structure. If rman_init() fails to initalize the mutex, it will
return ENOMEM; otherwise it will return 0 and rm will be initalized.
The rman_fini() function frees any structures associated with the
structure pointed to by the rm argument. If any of the resources within
the managed region have the RF_ALLOCATED flag set, it will return EBUSY;
otherwise, any mutexes associated with the structure will be released and
destroyed, and the function will return 0.
The rman_manage_region() function establishes the concept of a region
which is under rman control. The rman argument points to the region
descriptor. The start and end arguments specify the bounds of the
region. If successful, rman_manage_region() will return 0. If the
region overlaps with an existing region, it will return EBUSY. ENOMEM
will be return when rman_manage_region() failed to allocate memory for
the region.
The rman_reserve_resource_bound() function is where the bulk of the rman
logic is located. It attempts to reserve a contiguous range in the
specified region rm for the use of the device dev. The caller can
specify the start and end of an acceptable range, as well as alignment,
and the code will attempt to find a free segment which fits. The start
argument is the lowest acceptable starting value of the resource. The
end argument is the highest acceptable ending value of the resource.
Therefore, start + count - 1 must be ≤ end for any allocation to happen.
The default behavior is to allocate an exclusive segment, unless the
RF_SHAREABLE or RF_TIMESHARE flags are set, in which case a shared
segment will be allocated. If this shared segment already exists, the
caller has its device added to the list of consumers.
The rman_reserve_resource() function is used to reserve resources within
a previously established region. It is a simplified interface to
rman_reserve_resource_bound() which passes 0 for the flags argument.
The rman_make_alignment_flags() function returns the flag mask
corresponding to the desired alignment size. This should be used when
calling rman_reserve_resource_bound().
The rman_release_resource() function releases the reserved resource r.
It may attempt to merge adjacent free resources.
The rman_activate_resource() function marks a resource as active, by
setting the RF_ACTIVE flag. If this is a time shared resource, and the
caller has not yet acquired the resource, the function returns EBUSY.
The rman_deactivate_resource() function marks a resource r as inactive,
by clearing the RF_ACTIVE flag. If other consumers are waiting for this
range, it will wakeup their threads.
The rman_await_resource() function performs an asynchronous wait for a
resource r to become inactive, that is, for the RF_ACTIVE flag to be
cleared. It is used to enable cooperative sharing of a resource which
can only be safely used by one thread at a time. The arguments pri and
timo are passed to the rman_await_resource() function.
The rman_get_start(), rman_get_end(), rman_get_size(), and
rman_get_flags() functions return the bounds, size and flags of the
previously reserved resource r.
The rman_set_bustag() function associates a bus_space_tag_tt with the
resource r. The rman_get_bustag() function is used to retrieve this tag
once set.
The rman_set_bushandle() function associates a bus_space_handle_th with
the resource r. The rman_get_bushandle() function is used to retrieve
this handle once set.
The rman_set_virtual() function is used to associate a kernel virtual
address with a resource r. The rman_get_virtual() function can be used
to retrieve the KVA once set.
The rman_set_rid() function associates a resource identifier with a
resource r. The rman_get_rid() function retrieves this RID.
The rman_get_device() function returns a pointer to the device which
reserved the resource r.